Electromagnetic drive for photographic shutter diaphragms

ABSTRACT

An electromagnetic drive is provided for moving the blades or leaves of a photographic diaphragm, to adjust it to the desired aperture. The drive comprises a pot shaped magnet having an annular gap through which a cylindrical coil moves. The movement of the coil is mechanically connected to the diaphragm leaves or blades to set them to the desired position. The current flowing through the coil is controlled by an electrical bridge which, when balanced, stops the flow of current, the bridge circuit being influenced by either a position-sensitive resistor having a slider movable to various positions by the movement of the coil, or by a photo-sensitive resistor (photo-electric converter) placed behind the diaphragm so as to be responsive to variations in light resulting from changes in aperture produced by movement of the coil. Such a converter placed behind the diaphragm may also be regarded as a &#39;&#39;&#39;&#39;position-sensitive resistor&#39;&#39;&#39;&#39; since it is sensitive to the aperture position of the diaphragm. A latch is provided for latching the moving parts in position when the bridge circuit is balanced, to prevent or reduce overswing of the parts due to inertia. The invention is intended for still cameras, rather than motion picture cameras.

United States Patent 91 Mielke [451 May 21, 1974 ELECTROMAGNETIC DRIVE FOR PHOTOGRAPHIC SHUTTER DIAPHRAGMS [75] Inventor: Bodo Mielke, Wolfenbuttel, Germany [73] Assignee: Rollei-Werke Franke & Heidecke,

Braunschweig, Germany [22] Filed: Feb. 26, 1973 [21] Appl. No.: 335,914

Related US. Application Data [63] Continuation-impart of Ser. No. l55,4l5,, June 22,

l97l, Pat. No. 3,724,350.

[30] Foreign Application Priority Data June 26, I970 Germany 203l565 [52] US. Cl 95/64 D, 95/10 CD [51 Int. Cl. G03b 7/08, G03b 9/02 [58] Field of Search 95/lO C, 10 CE, 10 CD, 95/64 D [56] References Cited UNITED STATES PATENTS 3,554,633 l/l97l Sekine 95/64 D 2,973,699 3/l96l 3,657,987 4/1972 Babcock et al. 95/64 D 3,082,674 3/1963 Bagby 95/64 D 3,547,017 12/1970 Harvey 95/64 D Primary ExaminerJoseph F. Peters, Jr. Attorney, Agent, 'or Firm-Stonebaker & Shepard 5 7] ABSTRACT An electromagnetic drive is provided for moving the blades or leaves of a photographic diaphragm, to adjust it to the desired aperture. The drive comprises a pot shaped magnet having an annular gap through which a cylindrical coil moves. The movement of the coil is mechanically connected to the diaphragm leaves or blades to set them to the desired position. The current flowing through the coil is controlled by an electrical bridge which, when balanced, stops the flow of current, the bridge circuit being influenced by either a position-sensitive resistor having a slider movable to various positions by the movement of the coil, or by a photo-sensitive resistor (photo-electric converter) placed behind the diaphragm so as to be responsive to variations in light resulting from changes in aperture produced by movement of the coil. Such a converter placed behind the diaphragm may also be regarded as a position-sensitive resistor since it is sensitive to the aperture position of the diaphragm. A latch is provided for latching the moving parts in position when the bridge circuit is balanced, to prevent or reduce overswing of the parts due to inertia. The invention is intended for still cameras, rather than motion picture cameras.

ll Claims, 5 Drawing Figures 'EATENTEUMAY 21 m4 3.812.501

SHEEI 1 0F 4 Fig. 1

PATENTED MAY 2 1 .IBM

wumsum ELECTROMAGNETIC DRIVE FOR PI-IOTOGRAPHIC SHUTTER DIAPHRAGMS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my application Ser. No. 155,415, filed June 22, 1971, now U.S. Pat. No. 3,724,350 granted Apr. 3, 1973.

BACKGROUND OF THE INVENTION In the above mentioned application Ser. No. 55,415, there is disclosed an electromagnetic drive for a photographic shutter, employing a pot-shaped magnet with an annular gap through which a cylindrical coil moves, the coil being connected to the shutter blades so that when current is applied to the coil to cause it to move through the gap of the magnet, such movement of the coil will operate the shutter blades to open or close the shutter.

The present application deals with the use of such a magnet and moving coil to operate the diaphragm leaves or blades, as distinguished from the shutter blades. A quite different problem is involved in driving diaphragm leaves, as distinguished from shutter blades. In a shutter, the blades are ordinarily moved rapidly through a full stroke, either in an opening direction or a closing direction, intermediate positions of the blades not being involved except in a few special types of shutters. But the diaphragm leaves, on the contrary, are ordinarily not moved through a full stroke from maximum aperture to minimum aperture or vice versa, but are moved through only part of the distance, for example from a maximum aperture position to some intermediate aperture position which is desired for making a particular photographic exposure. Hence there is a problem of accurately controlling the extent of movement, so as to set the diaphragm at a particular aperture desired for a given exposure. Also, since the movement must be stopped at an intermediate point of the full range of travel of the parts, there is the problem of stopping the movement accurately at the desired point, in a way to eliminate or minimize the tendency to overrun on account of the inertia of the moving parts, and to eliminate or minimize the hunting likely to occur when there is an electrical feed-back dependent on the position to which the parts overrun on account of the inertia effect.

These problems or difficulties are overcome according to the present invention, in ways which will be apparent as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic illustration of a construction in accordance with the invention, showing the magnet in diametrical section and showing the moving coil and the diaphragm adjusting parts in schematic plan, with parts broken away;

FIG. 2 is a wiring diagram of an electrical bridge circuit for controlling the flow of current in the coil of the magnet, showing schematically a mechanical connection between the moving coil and a position-sensitive resistor;

FIG. 3 is a similar circuit diagram using a photoelectric converter situated behind the diaphragm, instead of a position-sensitive resistor mechanically connected to the coil;

FIG. 4 is a schematic plan of a-mechanical connection between the moving coil and the diaphragm leaves, embodying a latch for minimizing overrun due to inertia of the moving parts, the parts being shown in unlatched position with the diaphragm leaves at maximum aperture; and

FIG. 5 is a similar view showing the parts latched when the diaphragm leaves have been moved to a selected intermediate aperture.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is known in the art to use an electrical bridge circuit for photographic exposure measurement or control, either the exposure time (shutter speed) or the diaphragm aperture being automatically set under the control of the bridge. The present disclosure proceeds on the assumption that the reader is already familiar with such electrical bridges, so that the bridge circuitry does not have to be described in detail.

The use of a high speed moving coil for driving shutter blades is disclosed in the above mentioned parent application, Ser. No. 155,415, of which the present application is a continuation-in-part. The coil used in the present application for driving the diaphragm leaves is similar to the coil of the parent application, and the disclosure of the parent application is incorporated herein by reference. Also, the reader should refer to the various prior patents officially cited as references in the parent case, showing various prior attempts to control diaphragm apertures as well as shutter blades by the movement of electrical coils.

Referring now to FIG. 1 of the drawings, this first embodiment of the invention comprises a magnetic drive unit indicated in general at 3 and a diaphragm unit indicated in general at 7. The magnetic drive unit 3 is formed by a pot-shaped magnet 1, with a stationary central core 1a. The cylindrical coil 4 moves axially through the annular gap of the magnet when the coil is supplied with current through the circuit connections d and e. A guiding stem 40 fixed to the coil 4 moves in a stationary guide 2.

A contact member 5, mounted on and moving with but insulated from the coil 4, has a contact end which slides over a position-sensitive resistor, the combination of the resistor and the sliding contact being indicated in general at 6. The sliding contact is connected into the electrical circuitry at a, while the opposite ends of the position-sensitive resistor are electrically connected into the circuitry at b and c.

The magnetic drive 3 is mechanically connected to the diaphragm unit 7 by an arm 12 fixed to the moving coil to move with it, having a slot receiving a pin 13 on the diaphragm drive ring 11, only a fragment of which is shown. By means of the usual conventional pin and slot connections, the diaphragm drive ring 11 is connected to the diaphragm leaves 14, only one of which is shown, so that when the ring 1 1 turns (about the optical axis as a center) in one direction, the diaphragm leaves are swung toward maximum aperture, and when it turns in the opposite direction, the diaphragm leaves are swung toward minimum aperture.

The diaphragm drive ring 11 is provided on its outer periphery with an indicator or pointer projection 8 which moves in an arc over a diaphragm aperture scale 9, in accordance with the length of the stroke of the cylindrical coil 4. The scale 9 is graduated to show the usual f stop numbers, and also has an additional scale marking A representing the position for automatic setting of the diaphragm. A second indicator pointer on a manually settable diaphragm selector ring also moves over the diaphragm scale 9. A lug on this selector ring 10 forms a stop or abutment for engaging the left hand flank or edge of the indicator or pointer 8 on the diaphragm drive ring 11, and thus serves to limit the extent to which the diaphragm drive ring 11 can turn counterclockwise when the coil 4 moves in a corresponding direction (downward when viewed as in FIG. 1).

The operation is as follows: the diaphragm selector ring 10 is set to the desired diaphragm aperture if the operator wishes to select the aperture to be used, or is set to the position A if the operator desires automatic setting of the aperture. In the position A the indicator 8 of the blade drive ring 11 has the widest possible selection range, for the automatic setting of the correct diaphragm aperture. The photo-electric converter 15, shown in the electrical circuit diagram, FIG. 2, now determines, together with the position-sensitive resistor 6, the magnitude of the diaphragm aperture to be set.

When the conventional camera release is actuated to initiate the exposure cycle, immediately before the actual exposure an electric impulse is transmitted, through the circuitry shown in FIG. 2, to the connections d and e of the cylindrical moving coil 4, and continues as long as the electrical bridge is out of balance. The movement of the coil moves the position of the central contact or slider contact 5 (represented in FIG. 2 by a along the position-sensitive resistor, which thereby changes the resistance of a portion of the circuit as will be apparent from FIG. 2, and this change in resistance continues until the bridge circuit is in balance. It will be recalled that one arm of the bridge circuit includes the photo-electric converter 15, which is responsive to the amount of light falling on the converter, so that the balancing of the bridge circuit is dependent upon the amount of light. When the movement of the coil 4 reaches the point where the bridge circuit is in balance, the flow of current through the coil stops, and the movement accordingly stops. While it is moving, the coil 4 carries with it the diaphragm blade drive ring 11, by means of the pin and slot connection 12, 13. The drive ring 11 drives the diaphragm blades or leaves 14 in the known manner, usually closing the diaphragm down from maximum aperture to some other aperture at which the bridge is balanced, although the mechanism could operate, if desired, in the reverse direction, to open the diaphragm up from minimum aperture to the aperture at which the bridge is balanced. The pointer 8 on the ring 11 moves along the diaphragm scale 9 while the motion of thecoil 4 continues, and when it comes to rest, it shows the operator the value of the aperture which has been automatically set by the balancing bridge.

If the operator prefers to select the diaphragm aperture himself, rather than have it set automatically by the balancing bridge, this can be done. The diaphragm selector ring 10 is moved manually to the desired position, with the pointer on this ring pointing to the selected aperture. As shown in FIG. 2, the bridge circuit contains a switch 18, which is normally open so long as the selector ring 10 is in the A or automatic position, and which is closed whenever the selector ring is moved away from the A position. The closing of the switch 18 serves to de-tune the bridge circuit in such a way that even under very unfavorable light conditions, the indicator 8 of the blade drive ring 11 will be drawn, during the operating cycle, against the stop 15 of the diaphragm selector ring 10, so that the movement of the coil 4 can continue only until the diaphragm is closed down to the aperture selected by the operator.

FIG. 2 illustrates schematically the main elements of the bridge circuit for the electromagnetic drive. The portion marked 6 in FIG. 2 represents the positionsensitive resistor with its electrical connections a, b, and c. The mechanical connection between the moving coil and the slider of the resistor, shown mechanically in FIG. 1, is indicated schematically in FIG. 2 by the broken line. The moving coil 4 is electrically connected to the output of the bridge through the connections d and e. In addition to the two transistor diode circuits situated symmetrically with respect to the moving coil 4, one branch of the bridge contains the photo-electric converter 15, and the other the time-setting potentiometer 16 and the film speed setting potentiometer 17. In this circuit system the photo-electric converter 15 is arranged as an external exposure measurement transmitter. The switch 18 serves to de-tune the bridge and is switched on (that is, closed) automatically as soon as the diaphragm selector ring 10 is moved away from the position A for the purpose of manual diaphragm selection.

FIG. 3 shows a similar bridge circuit which omits the position-sensitive resistor 6. In this modification illustrated in FIG. 3, the correct diaphragm aperture is selected by the indirect coupling (shown schematically by the broken line) of the moving coil 4 with the photoelectric converter 15. This photo-electric converter 15 is in the present case installed not as an external exposure measuring transmitter, but as an internal exposure measuring transmitter, behind the lens system and behind the diaphragm which is included in the lens system. Every movement of the coil 4 and corresponding movement of the diaphragm blades or leaves 14 is registered by the photo-electric converter 15 and contrib utes to the bridge de-tuning process. That is, the change in the diaphragm aperture changes the amount of light falling on the converter element 15, and thus there is a feed back, the movement of the coil influencing the balancing of the bridge because it influences the amount of light falling on the element 15 and thereby changes the resistance of the arm of the bridge which contains the element 15.

In this modified arrangement shown in FIG. 3, the positionsensitive resistor arrangement 6 of FIG. 2 has been replaced by the setting potentiometer 19. The setting potentiometer 19 is adjustable within a wide range, and influences the sensitivity of the bridge circuit. All other elements of the bridge circuit are substantially the same as those shown in FIG. 2.

The term position-sensitive resistor is intended, of course, to refer to a resistor so arranged that the resistance of some circuit including all or part of this resistor varies with a variable position of some part. In the resistor arrangement 6 shown in FIGS. 1 and 2, this is obviously true, since the resistance of part of the circuit will vary according to the position of the slider a (or 5) on the resistance element. But it is pointed out that when the photo-electric converter 15 is placed behind the diaphragm, as in FIG. 3, then the photo-electric converter may also be considered, broadly, as a position-sensitive resistor, since the resistance varies according to the position of the diaphragm leaves or blades which control the amount of light falling on the element 15. Hence the term position-sensitive resistor as used in the claims is intended to be broad enough to include the photo-electric converter when it is placed behind the diaphragm, as well as including the resistor and slider arrangement 6. The term does not, however, include a photo-electric converter which is not placed behind the diaphragm and is not sensitive to the position of some part of the mechanism.

FIGS. 4 and 5 illustrate a modified form of mechanical connection between the moving coil and the diaphragm driving ring, this modified connection being designed to eliminate or at least reduce the overrun or overswing which may occur when the parts have moved far enough to balance the electrical bridge and cut off the flow of current through the coil, the movement tending to continue somewhat beyond this point because of the inertia of the moving parts. Referring to FIG. 4, the magnet is shown as before at l, and the stem of the moving coil is shown at 4a. Just as in the case of FIG. 1, the drive ring for driving the diaphragm blades or leaves is shown at 11, and one of the diaphragm leaves is indicated at 14. There are, of course, several of such leaves or blades, as well understood in the art, only one being illustrated.

In this construction, the pin and slot connection l2, 13 between the coil and the drive ring, shown in FIG. 1, is eliminated. In place of this, the stem or rod 4a of the moving coil is provided with a driving pin 41. On a fixed pivot 51 a lever 61 is pivoted, and has a groove or slot 71in which the pin 41 is loosely received with some play. The free end of the lever 61 is constructed as a fork with a longitudinal slot 81 extending radially with respect to the pivot 51. This slot 81 receives snugly, without lateral play, a circular pin 91 on the blade ring 11. The diaphragm leaves or blades or seetors areclosed down toward minimum aperture when the lever 61 swings downwardly in response to downward movement of the coil stem 40 in the direction of the arrow A in FIG. 4, to swing the diaphragm ring 11 in a clockwise direction, and the sectors are opened up toward maximum aperture when the coil stem 4a moves upwardly.

As already mentioned, the groove or slot 71 in the lever 61 is wider than the diameter of the pin 41, so that there is some play in the connection of the coil stem 4a to the lever 61. When the coil is energized through the electrical bridge connections, to move the stem 4a downwardly in the direction of the arrow A, the pin 41 rests on and pushes against the lower edge of the groove 71. When the motion has proceeded far enough to bring the electric bridge into balance, the current in the coil 4 stops, and the coil and its stem 4a tend to come to a stop, but the heavier moving parts, such as the diaphragm driving ring 11, the leaves or sectors 14, and the lever 61, tend to continue their movement on account of the inertia effect, so that the upper edge of the groove or slot 71 now comes into contact with the pin 41.

A pawl 112 is pivotally mounted on a pin 113 on the lever 61, and has a fork portion with a slot 114 which snugly receives the driver pin 41, without clearance. The pointed end 115 of the pawl, during the diaphragm setting operation, moves in the arc of a circle around the center of the pin 51. A fixed toothed segment 116 with the same radius is arranged in such a manner that the pawl swings along it, close to but without engaging the teeth 117 of the segment 116. At the balancing point (that is, at the point in the movement of the parts when the electrical bridge becomes balanced) where the movement of the lever 61 overtakes the coil stem 4a as a result of inertia, the point 115 of the pawl 112 is thrust into the teeth 117 of the toothed segment 116, thus locking the sector drive and preventing any further overrun of the diaphragm sector ring 11.

To insure that this locking process will not be repeated when the coil stem 4a is drawn back (that is, 1

the pawl 1'12 and the lever 61, and the pivot pin 113 on which the pawl is mounted is preferably engaged in a slightly oval or elongated opening 119 in the pawl, as shown.

FIG. 4 shows the parts in unlocked position, with the diaphragm sectors fully open, ready for a closing down operation. FIG. S illustrates, in full lines, the locking action when the moving parts reach a certain intennediate position when the electrical bridge becomes balanced. It will be seen that the inertia effect has pulled the bottom edge of the slot 71 slightly away from the bottom of the drive pin 41, and the top of the drive pin 41 has reacted against the top edge of the slot 114 on the pawl 112, to turn the pawl slightly clockwise on its pivot 113, to bring the end 115 of the pawl into locking engagement with the teeth 117 on the sector 116. During the subsequent upward movement of the coil 4 at the conclusion of the exposure, the drive pin 41 will pull further upwardly on the pawl and this force, aided by the spring 118, will pull slightly upwardly on the pawl (this being permitted by the elongation of the opening 119) to unlock the pawl from the toothed segment 117, to permit the upward movement to restore diaphragm leaves or sectors to fully open position. FIG. 5 also illustrates, in broken lines, a different position of the parts, wherein the sectors would be further closed down toward the minimum aperture.

This latching arrangement stops the motion of the moving parts so close to the theoretically correct position that there is ordinarily no appreciable tendency of the drive system to withdraw or back-up to the exact balancing point, and thus no hunting of the system. Hence the present invention provides a very fast diaphragm setting arrangement for still cameras, for it is not necessary to allow extra time for hunting to cease, before opening the shutter .to make the actual exposure.

What is claimed is:

1. An electromagnetic drive for photographic shutter diaphragms comprising:

a pot-shaped magnet having an annular gap;

a cylindrical coil movable axially through said annular gap in response to electric current flowing through said coil; 1

an electric bridge having circuit means for supplying current to said coil when said bridge is out of balance and for discontinuing supply of current to said coil when said bridge is in balance;

said circuit means of said bridge including a positionsensitive resistor;

a diaphragm including means for varying the aperture thereof;

means operatively connecting said coil to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil;

and means operated by movement of said coil for varying the effective resistance of said resistor in said circuit means, thereby to vary the balance of said bridge.

2. A drive as defined in claim 1, wherein said position-sensitive resistor has a movable slider connected to said coil to move therewith.

3. A drive as defined in claim 1, wherein said position-sensitive resistor is a photo-electric converter situated behind said diaphragm so that variation of the aperture position of said diaphragm, caused by movement of said coil, will vary the amount of light reaching said photo-electric converter, thereby varying the effective resistance of said converter in said circuit means.

4. A drive as defined in claim 1, further including latchmeans operated by inertia effect of said aperture varying means tending to continue to move after supply of current to said coil has been discontinued, for latching said aperture varying means against further movement.

5. A drive as defined in claim 1, whereinsaid means operatively connecting said coil to said aperture varying means includes means providing limited play between said coil and said aperture varying means, so that when said coil tends to stop moving upon discontinuance of flow of current therein, said aperture varying means may overrun and continue to move to a limited extent, said drive further including a stationary toothed segment, a pawl mounted on and moving with said connecting means, and means operated by said overrun for engaging said pawl with said toothed segment. I

6. A drive as defined in claim 1, wherein said aperture varying means includes a diaphragm drive ring (11), and wherein said means operatively connecting said coil to said aperture varying means includes a coupling lever (61) having a snug connection (81, 91) with said drive ring (11) and having a non-snug pin and slot connection (41, 71) with said coil, with limited play in said pin and slot connection, said drive further including a fixed segment (116) having teeth (117) thereon,-

and a latching pawl (112) pivotally mounted on said coupling lever and having a snug connection (41, 114) with said coil, said pawl having a tooth (115) adapted to engage said teeth (117 of said segment when said pawl is swung to a certain position relative to said coupling lever on which it is mounted, the snug connection of said coil to said pawl and the play connection of said coil to said coupling lever being so related to each other that when the coil tends to stop moving and the coupling lever tends to continue moving, due to inertia, to the limited extent permitted by said play connection, the snug connection of said pawl with said coil will move said pawl to said certain position, to engage the pawl with said fixed segment and stop further movement of said coupling lever and parts snugly connected thereto. Y

7. A drive as defined in claim 1, wherein said circuit means of said electric bridge includes a branch having therein a photo-electric converter (15), a shutter speed setting-potentiometer (16), and a film speed setting potentiometer (l7).

8. An electromagnetic drive for photographic shutter diaphragms comprising:

a pot-shaped magnet having an annular gap;

a cylindrical coil movable axially through said annular gap in response to electric current flowing through-said coil;

a diaphragm including means for varying the aperture thereof;

a position-sensitive resistor operatively connected to influence the flow of current through said coil;

means operatively connectingsaid coil to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil;

and means operated by movement of said coil for varying the effective resistance of said resistor, thereby to influence the flow of current through said coil.

9. An electromagnetic drive fora photographic diaphragm comprising a coil and magnet assembly including a coil and a magnet movable relative to each other in response to flow of current through said coil, means including an electric bridge for supplying current to said coil when said bridge is out of balance and for discontinuing supply of current to said coil when said bridge is in balance, a diaphragm having means for varying the aperture of the diaphragm, means operatively connecting said coil and magnet assembly to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil and magnet relative to each other, and latch means operated by inertia effect of said aperture varying means tending to continue to move after supply of current to said coil has been discontinued, for latching said aperture varying means against further movement.

10. A drive as defined in claim 9, wherein said means operatively connecting said assembly to said aperture varying means includes means providing limited play between said assembly and said aperture varying means, so that when relative movement of saidassembly' tends to stop upon discontinuance of flow of current in said coil, said aperture varying means may overrun and continue to move to a limited extent, said latch means including a stationary toothed segment, a pawl mounted on and moving with said connecting means, and means operated by said overrun for engaging said pawl with said toothed segment.

11. A drive as defined in claim 9, wherein said aperture varying means includes a diaphragm drive ring, and wherein said means operatively connecting said assembly to said aperture varying means includes a cou pling lever having a snug connection with said drive ring and having a non-snug pin and slot connection with said assembly, with limited play in said pin and slot connection, and wherein said latch means includes a fixed segment having teeth thereon, and a latching pawl pivotally mounted on said coupling lever and having a snug connection with said assembly, said pawl having a tooth adapted to engage said teeth of said segment when said pawl is swung to a certain position relative to said coupling lever on which it is mounted, the snug connection of said assembly to said pawl and the play connection of said assembly to said coupling lever being so related to each other that when relative motion in said assembly tends to stop and the coupling lever tends to continue moving, due to inertia, to the limited extent permitted by said play connection, the

snug connection of said pawl will move said pawl to said certain position, to engage the pawl with said fixed segment and stop further movement of said coupling lever and parts snugly connected thereto. 1:

UNITED STATES PATENT OFFICE U CERTIFICATE OF CORRECTION Patent No 501 Dated." May 2i 1974 Bodo Miolko Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet item [30] line 1, "2031565" should read P 20 31 565.5 same item [30] insert March 2, 1972 Germany P 22 09 913.4 October 28, 1972 Germany P 22 52 9 92.6

Column 1, line 12', "55,415" should read 155,415

Signed and sealed this 8th day of October 1974.

(SEAL) Attes t1 McCOY M. GIBSON JR. (3. MARSHALL DANN Attestin'g Officer Commissioner of Patents F ORM po'wso (m'eg) USCOMM-DC wave-ps9 11.5 GOVERNMENT HUNTING OFF CE 93 o Patent No g a Dated y 2 1974 Inventor(s,) Bode Mlclke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet item [30], line 1, "2031565" should read P 20 31 565 5 same item [30] insert March 2 1972 Germany a P 22 '09 91344 October 28, 1972 Germany P 22 52 9 92.6 Column 1, line 112', "55,415" should read 1555415 Signed and sealed this 8th day of October 1974.

(SQ-XL) Attes t:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM FO-105O (10 69) I USOMMDC 5 16.

"'5 GOVERNMENT HUNTING OFFICE: 9. 93 

1. An electromagnetic drive for photographic shutter diaphragms comprising: a pot-shaped magnet having an annular gap; a cylindrical coil movable axially through said annular gap in response to electric current flowing through said coil; an electric bridge having circuit means for supplying current to said coil when said bridge is out of balance and for discontinuing supply of current to said coil when said bridge is in balance; said circuit means of said bridge including a position-sensitive resistor; a diaphragm including means for varying the aperture thereof; means operatively connecting said coil to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil; and means operated by movement of said coil for varying the effective resistance of said resistor in said circuit means, thereby to vary the balance of said bridge.
 2. A drive as defined in claim 1, wherein said position-sensitive resistor has a movable slider connected to said coil to move therewith.
 3. A drive as defined in claim 1, wherein said position-sensitive resistor is a photo-electric converter situated behind said diaphragm so that variation of the aperture position of said diaphragm, caused by movement of said coil, will vary the amount of light reaching said photo-electric converter, thereby varying the effective resistance of said converter in said circuit means.
 4. A drive as defined in claim 1, further including latch means operated by inertia effect of said aperture varying means tending to continue to move after supply of current to said coil has been discontinued, for latching said aperture varying means against further movement.
 5. A drive as defined in claim 1, wherein said means operatively connecting said coil to said aperture varying means includes means providing limited play between said coil and said aperture varying means, so that when said coil tends to stop moving upon discontinuance of flow of current therein, said aperture varying means may overrun and continue to move to a limited extent, said drive further including a stationary toothed segment, a pawl mounted on and moving with said connecting Means, and means operated by said overrun for engaging said pawl with said toothed segment.
 6. A drive as defined in claim 1, wherein said aperture varying means includes a diaphragm drive ring (11), and wherein said means operatively connecting said coil to said aperture varying means includes a coupling lever (61) having a snug connection (81, 91) with said drive ring (11) and having a non-snug pin and slot connection (41, 71) with said coil, with limited play in said pin and slot connection, said drive further including a fixed segment (116) having teeth (117) thereon, and a latching pawl (112) pivotally mounted on said coupling lever and having a snug connection (41, 114) with said coil, said pawl having a tooth (115) adapted to engage said teeth (117) of said segment when said pawl is swung to a certain position relative to said coupling lever on which it is mounted, the snug connection of said coil to said pawl and the play connection of said coil to said coupling lever being so related to each other that when the coil tends to stop moving and the coupling lever tends to continue moving, due to inertia, to the limited extent permitted by said play connection, the snug connection of said pawl with said coil will move said pawl to said certain position, to engage the pawl with said fixed segment and stop further movement of said coupling lever and parts snugly connected thereto.
 7. A drive as defined in claim 1, wherein said circuit means of said electric bridge includes a branch having therein a photo-electric converter (15), a shutter speed setting potentiometer (16), and a film speed setting potentiometer (17).
 8. An electromagnetic drive for photographic shutter diaphragms comprising: a pot-shaped magnet having an annular gap; a cylindrical coil movable axially through said annular gap in response to electric current flowing through said coil; a diaphragm including means for varying the aperture thereof; a position-sensitive resistor operatively connected to influence the flow of current through said coil; means operatively connecting said coil to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil; and means operated by movement of said coil for varying the effective resistance of said resistor, thereby to influence the flow of current through said coil.
 9. An electromagnetic drive for a photographic diaphragm comprising a coil and magnet assembly including a coil and a magnet movable relative to each other in response to flow of current through said coil, means including an electric bridge for supplying current to said coil when said bridge is out of balance and for discontinuing supply of current to said coil when said bridge is in balance, a diaphragm having means for varying the aperture of the diaphragm, means operatively connecting said coil and magnet assembly to said aperture varying means, to vary the aperture of the diaphragm by movement of said coil and magnet relative to each other, and latch means operated by inertia effect of said aperture varying means tending to continue to move after supply of current to said coil has been discontinued, for latching said aperture varying means against further movement.
 10. A drive as defined in claim 9, wherein said means operatively connecting said assembly to said aperture varying means includes means providing limited play between said assembly and said aperture varying means, so that when relative movement of said assembly tends to stop upon discontinuance of flow of current in said coil, said aperture varying means may overrun and continue to move to a limited extent, said latch means including a stationary toothed segment, a pawl mounted on and moving with said connecting means, and means operated by said overrun for engaging said pawl with said toothed segment.
 11. A drive as defined in claim 9, wherein said aperture varying means includes a diaphragm drive ring, and wherein said means operatively connecting said assembly To said aperture varying means includes a coupling lever having a snug connection with said drive ring and having a non-snug pin and slot connection with said assembly, with limited play in said pin and slot connection, and wherein said latch means includes a fixed segment having teeth thereon, and a latching pawl pivotally mounted on said coupling lever and having a snug connection with said assembly, said pawl having a tooth adapted to engage said teeth of said segment when said pawl is swung to a certain position relative to said coupling lever on which it is mounted, the snug connection of said assembly to said pawl and the play connection of said assembly to said coupling lever being so related to each other that when relative motion in said assembly tends to stop and the coupling lever tends to continue moving, due to inertia, to the limited extent permitted by said play connection, the snug connection of said pawl will move said pawl to said certain position, to engage the pawl with said fixed segment and stop further movement of said coupling lever and parts snugly connected thereto. 